Multiplexer, radio-frequency front end circuit, and communication apparatus

ABSTRACT

A multiplexer includes a common terminal, a first terminal, a second terminal, and a third terminal, a first filter, a second filter, and a third filter. With a frequency f3 being defined as M×f1±N×f2 or M×f2±N×f1, M and N being natural numbers, f1 being a frequency included in a first passband of the first filter and f2 being a frequency included in a second passband of the second filter, at least a part of a range of frequency f3 overlaps a third passband of the third filter. No acoustic wave resonator is connected between the common terminal and a first parallel arm resonance circuit. A fractional bandwidth of the first parallel arm resonance circuit is smaller than a maximum value of a fractional bandwidth of each of at least one serial arm resonance circuit.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Japanese patent applicationserial no. 2018-240955, filed in the Japanese Patent Office on Dec. 25,2018, the entire contents of which being incorporated herein byreference. Also, the present application contains subject matter relatedto that in U.S. application Ser. No. ______, entitled Multiplexer,Radio-Frequency Front End Circuit, and Communication Apparatus, havingcommon inventorship and bearing Attorney docket number 13449US01, theentire contents of which being incorporate herein by reference.

BACKGROUND Technical Field

The present disclosure relates to a multiplexer capable of transmittingsignals in a plurality of frequency bands, a radio-frequency front endcircuit, and a communication apparatus.

Description of the Background Art

A multiplexer capable of transmitting signals in a plurality offrequency bands has conventionally been known. For example, JapanesePatent Laid-Open No. 2017-152881 discloses a multiplexer including twotransmission filters, two reception filters, and one transmission andreception filter. As inductance elements are arranged in series betweenone of the plurality of filters and a common terminal, insertion loss ina passband of each filter can be reduced even though the number offrequency bands used by the multiplexer is increased.

SUMMARY

Each of the plurality of filters included in the multiplexer disclosedin Japanese Patent Laid-Open No. 2017-152881 is an acoustic wave filterformed from an acoustic wave resonator. An elastic constant of theacoustic wave resonator has been known to be non-linear. Whenintermodulation distortion (IMD) of two transmission signals originatingfrom such non-linearity occurs in a frequency band of a receptionsignal, reception sensitivity of the multiplexer is deteriorated. Asrecognized by the present inventor, Japanese Patent Laid-Open No.2017-152881, however, is silent about deterioration of receptionsensitivity due to IMD of two transmission signals.

The present disclosure was made to solve the problem recognized by thepresent inventor, as described above, and therefore an aspect of thepresent disclosure is to suppress deterioration of reception sensitivityof a multiplexer.

A multiplexer according to the present disclosure includes a commonterminal, a first terminal, a second terminal, and a third terminal, afirst filter, a second filter, and a third filter. The first filter isconnected between the common terminal and the first terminal and has afirst passband. The second filter is connected between the commonterminal and the second terminal and has a second passband notoverlapping the first passband. Passbands that do not overlap isintended to be construed with reference to filter characteristics of twofilters with passbands defined by their respective 3 dB points. Thethird filter is connected between the common terminal and the thirdterminal and has a third passband overlapping neither the first passbandnor the second passband. With a frequency f3 being defined as M×f1±N×f2or M×f2±N×f1, wherein M and N being natural numbers, f1 being afrequency included in the first passband and f2 being a frequencyincluded in the second passband, at least a part of a range of frequencyf3 overlaps the third passband. The first filter includes at least onefirst serial arm resonance circuit and a first parallel arm resonancecircuit. The at least one first serial arm resonance circuit isconnected between the common terminal and the first terminal. The firstparallel arm resonance circuit is connected between the common terminaland a grounding point and includes at least one acoustic wave resonator.No acoustic wave resonator is connected between the common terminal andthe first parallel arm resonance circuit. When a value calculated bydividing a difference between an antiresonance frequency and a resonancefrequency of a resonance circuit by the resonance frequency is definedas a fractional bandwidth of the resonance circuit, a fractionalbandwidth of the first parallel arm resonance circuit is smaller than amaximum value of a fractional bandwidth of each of the at least onefirst serial arm resonance circuit.

According to an exemplary multiplexer in the present disclosure, afractional bandwidth of the first parallel arm resonance circuit issmaller than a maximum value of a fractional bandwidth of each of atleast one first serial arm resonance circuit so that deterioration ofreception sensitivity can be suppressed.

The foregoing and other objects, features, aspects and advantages of thepresent disclosure will become more apparent from the following detaileddescription of the present disclosure when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit configuration diagram of a multiplexer according toa first embodiment.

FIG. 2 is a diagram showing a specific circuit configuration of atransmission filter in FIG. 1.

FIG. 3 is a chart showing relation between a resonance frequency and afractional bandwidth of a general acoustic wave resonator.

FIG. 4 is a diagram showing application of AC power to an acoustic waveresonator by an AC power supply.

FIG. 5 is a diagram expressing relation between AC power and excitationin the configuration shown in FIG. 4 by using an electric circuit and amechanical circuit.

FIG. 6 is an electrical equivalent circuit diagram of a BVD modelcorresponding to the acoustic wave resonator in FIG. 4.

FIG. 7 is a diagram showing a frequency characteristic of an impedanceof the acoustic wave resonator in FIG. 6 and also a frequencycharacteristic of a current that flows through the acoustic waveresonator.

FIG. 8 is a diagram showing variation in frequency characteristic of animpedance, variation in frequency characteristic of a current through anacoustic path, and also variation in frequency characteristic of acurrent density in the acoustic path when a fractional bandwidth of anacoustic wave resonator is varied with a damping capacitance of theacoustic wave resonator being constant.

FIG. 9 is a diagram showing correspondence between a duty ratio of anacoustic wave resonator and an IMD3 level.

FIG. 10 is a plan view schematically showing a structure of an electrodeof the acoustic wave resonator in FIG. 9.

FIG. 11 is a circuit configuration diagram of a multiplexer according toa first modification of the first embodiment.

FIG. 12 is a circuit configuration diagram of a multiplexer according toa second modification of the first embodiment.

FIG. 13 is an electrical equivalent circuit diagram of a BVD modelcorresponding to a parallel arm resonance circuit in FIG. 12.

FIG. 14 is a circuit configuration diagram of a multiplexer according toa second embodiment.

FIG. 15 is a diagram showing a specific circuit configuration of atransmission filter in FIG. 14.

FIG. 16 is a diagram showing a pass characteristic of the multiplexer inFIG. 15 and also a pass characteristic of a multiplexer according to afirst comparative example.

FIG. 17 is a circuit configuration diagram of a multiplexer according toa modification of the second embodiment.

FIG. 18 is a circuit configuration diagram of a multiplexer according toa third embodiment.

FIG. 19 is a diagram showing a pass characteristic of the multiplexer inFIG. 18 and also a pass characteristic of a multiplexer according to asecond comparative example.

FIG. 20 is a circuit configuration diagram of a multiplexer according toa modification of the third embodiment.

FIG. 21 is a circuit configuration diagram of a multiplexer according toa fourth embodiment.

FIG. 22 is a configuration diagram of a communication apparatusaccording to a fifth embodiment.

DESCRIPTION OF EMBODIMENTS

An embodiment will be described in detail below with reference to thedrawings. The same or corresponding elements in the drawings have thesame reference characters allotted and description thereof will not berepeated in principle. Connection between two circuit elementsencompasses both of direct connection between the two circuit elementsand indirect connection therebetween with another circuit element beinginterposed. A resonance circuit may be formed from a single resonator. Aresonance frequency of a resonance circuit refers to a frequency atwhich an impedance of the resonance circuit attains to a relativeminimum. An antiresonance frequency of a resonance circuit refers to afrequency at which an impedance of the resonance circuit attains to arelative maximum.

When a resonance circuit includes two or more acoustic wave resonatorsdifferent in resonance frequency from each other, an impedance of theresonance circuit attains a relative minimum at a resonance frequency ofeach acoustic wave resonator and a relative maximum at an antiresonancefrequency of each acoustic wave resonator. In this case, the resonancefrequency of the resonance circuit is a resonance frequency closest to acentral frequency of a filter including the resonance circuit, amongresonance frequencies of the acoustic wave resonators. The antiresonancefrequency of the resonance circuit is an antiresonance frequency closestto the central frequency of the filter including the resonance circuit,among antiresonance frequencies of acoustic wave resonators.

First Embodiment

FIG. 1 is a circuit configuration diagram of a multiplexer 1 accordingto a first embodiment. As shown in FIG. 1, multiplexer 1 includes acommon terminal T10 (a common terminal), a terminal T11 (a firstterminal), a terminal T12 (a second terminal), a terminal T13 (a thirdterminal), a transmission filter 101 (a first filter), a transmissionfilter 102 (a second filter), a reception filter 103 (a third filter),and a phase shifter 110.

Common terminal T10 is connected to phase shifter 110. Transmissionfilter 101 is connected to phase shifter 110 and terminal T11, betweencommon terminal T10 and terminal T11. Transmission filter 102 isconnected to phase shifter 110 and terminal T12, between common terminalT10 and terminal T12. Reception filter 103 is connected to phase shifter110 and terminal T13, between common terminal T10 and terminal T13.Phase shifter 110 may be provided as necessary and it is not anessential feature. Furthermore, the language “connected between” (in thecontext of a connection between two terminals, or a terminal and afilter) is used to describe a direct connection, or the optional phaseshifter 110 as part of the connection. Moreover, as an example,transmission filter 101 being connected between terminals T10 and T11,should be construed as meaning that the transmission filter 101 iseither directly connected to T10 and T11, or not (e.g., with the phaseshifter 110 inserted between filter 101 and terminal T10).

In multiplexer 1, a passband of transmission filter 101 (a firstpassband) and a passband of transmission filter 102 (a second passband)are each a frequency band of a transmission signal (a transmissionband). A passband of reception filter 103 (a third passband) is afrequency band of a reception signal (a reception band).

The passband of transmission filter 102 does not overlap the passband oftransmission filter 101. The passband of reception filter 103 overlapsneither of the passband of transmission filter 101 and the passband oftransmission filter 102.

Multiplexer 1 can simultaneously transmit a signal in the passband oftransmission filter 101 input from terminal T11 and a signal in thepassband of transmission filter 102 input from terminal T12. In otherwords, multiplexer 1 is adapted to 2 up link carrier aggregation(2ULCA).

FIG. 2 is a diagram showing a specific circuit configuration oftransmission filter 101 in FIG. 1. As shown in FIG. 2, transmissionfilter 101 includes serial arm resonators s1 to s3 (a first serial armresonance circuit), parallel arm resonators p1 to p3, and a parallel armresonator p4 (a first parallel arm resonance circuit). Transmissionfilter 101 is an acoustic wave filter formed from an acoustic waveresonator. Examples of the acoustic wave resonator include a surfaceacoustic wave (SAW) resonator, a bulk acoustic wave (BAW) resonator, afilm bulk acoustic wave resonator (FBAR), or a solidly mounted (SM)resonator.

Serial arm resonators s1 to s3 are connected in series in this orderbetween terminal T11 and phase shifter 110. Parallel arm resonator p1 isconnected between a grounding point and a connection node betweenterminal T11 and serial arm resonator s1. Parallel arm resonator p2 isconnected between the grounding point and a connection node betweenserial arm resonators s1 and s2. Parallel arm resonator p3 is connectedbetween the grounding point and a connection node between serial armresonators s2 and s3. Parallel arm resonator p4 is connected between thegrounding point and a connection node between serial arm resonator s3and phase shifter 110. No acoustic wave resonator is connected betweencommon terminal T10 and parallel arm resonator p4.

A transmission signal (a transmission signal in the first passband)input from terminal T11 passes through transmission filter 101 and isreflected by transmission filter 102 and reception filter 103 and outputfrom common terminal T10.

A transmission signal (a transmission signal in the second passband)input from terminal T12 passes through transmission filter 102 and isreflected by transmission filter 101 and reception filter 103 and outputfrom common terminal T10. Specifically, a current corresponding to thetransmission signal from transmission filter 102 is input totransmission filter 101 and divided into currents to parallel armresonator p4 and serial arm resonator s3. The transmission signal isreflected mainly by parallel arm resonator p4 and serial arm resonators3 and output from common terminal T10.

An elastic constant of an acoustic wave resonator has been known to benon-linear. Owing to such non-linearity, IMD of two transmission signalsof multiplexer 1 occurs. A frequency f3 of IMD is expressed as M×f1±N×f2or M×f2±N×f1 (M and N being natural numbers) where f1 represents afrequency included in the passband of transmission filter 101 and f2represents a frequency included in the passband of transmission filter102. When a part of a range of frequency f3 overlaps the passband ofreception filter 103, IMD occurs in a reception band of multiplexer 1 intransmission of the two transmission signals. In particular, third-orderintermodulation distortion (IMD3) where a condition of f3=2×f1−f2 orf3=2×f2−f1 is satisfied occurs in the vicinity of the two transmissionbands. Therefore, when the reception band is relatively close to the twotransmission bands, IMD3 often gives rise to a problem. Consequently,reception sensitivity of multiplexer 1 is deteriorated.

In multiplexer 1, a part of the range of frequency f3 of IMD3 expressedas 2×f1−f2 overlaps the passband of reception filter 103. Distortioncaused by non-linearity of the elastic constant of the acoustic waveresonator tends to be large as the resonance circuit is closer to commonterminal T10. In multiplexer 1, a fractional bandwidth of parallel armresonator p4 is set to be smaller than a maximum value of a fractionalbandwidth of each of serial arm resonators s1 to s3 so that a currentdensity in parallel arm resonator p4 is lower than a maximum value of acurrent density in each of serial arm resonators s1 to s3. Thefractional bandwidth of the acoustic wave resonator refers to a ratio ofa difference between an antiresonance frequency and a resonancefrequency to the resonance frequency. Since IMD due to the transmissionsignal from transmission filter 101 and the transmission signal fromtransmission filter 102 can be suppressed, deterioration of receptionsensitivity of multiplexer 1 can be suppressed. IMD that deterioratesreception sensitivity of multiplexer 1 is not limited to IMD3.

FIG. 3 is a graph of charted values showing a relation between aresonance frequency fr and a fractional bandwidth BWR of a generalacoustic wave resonator. As resonance frequency fr is varied, fractionalbandwidth BWR is varied. When a general acoustic wave filter isimplemented by a plurality of acoustic wave resonators, a difference inresonance frequency fr among the plurality of acoustic wave resonatorsis approximately not more than 100 MHz. As shown in FIG. 3, whenresonance frequency fr is varied by 100 MHz, fractional bandwidth BWR isvaried by approximately 0.7%. It is therefore assumed below that, when adifference between two fractional bandwidths is equal to or more than0.8%, the two fractional bandwidths are different and that when thedifference between the two fractional bandwidths is less than 0.8%, thetwo fractional bandwidths are equal to each other.

When an acoustic wave resonator is implemented by a SAW resonator, afractional bandwidth of the SAW resonator can be varied by providing afirst adjustment film composed of an insulator or a dielectric between acomb electrode and a piezoelectric substrate and varying a thickness ofthe first adjustment film. The fractional bandwidth is greatest in theabsence of the first adjustment film and is smaller as the firstadjustment film is larger in thickness. The fractional bandwidth of theSAW resonator can be varied by providing a second adjustment filmcomposed of an insulator or a dielectric to cover a comb electrode andvarying a thickness of the second adjustment film. The fractionalbandwidth is greatest in the absence of the second adjustment film andis smaller as the second adjustment film is larger in thickness.

When an acoustic wave resonator is implemented by a BAW resonator, afractional bandwidth can be varied by changing a material for apiezoelectric body between opposing electrodes.

Relation between intermodulation distortion and a current density willbe described below with reference to FIGS. 4 to 6. FIG. 4 is a diagramshowing application of alternating-current (AC) power to an acousticwave resonator 800 by an AC power supply 900. FIG. 4 shows BAW acousticwave resonator 800 by way of example of the acoustic wave resonator. Asshown in FIG. 4, acoustic wave resonator 800 includes an electrode 801,an electrode 802, and a piezoelectric body 803. Piezoelectric body 803is formed between electrode 801 and electrode 802. As AC power isapplied across electrodes 801 and 802, a voltage V1 corresponding to ACpower is generated across electrodes 801 and 802 and a current Iw isinput to acoustic wave resonator 800. Consequently, acoustic waveresonator 800 is excited at magnitude of force F1.

FIG. 5 is a diagram expressing relation between AC power and excitationin the configuration shown in FIG. 4 by using an electric circuit 811and a mechanical circuit 812. As shown in FIG. 5, electric circuit 811includes a capacitor C0 and an inductor L80. Capacitor C0 and inductorL80 are connected in parallel between opposing ends of AC power supply900. A capacity of capacitor C0 is a damping capacitance representing acapacitive component of acoustic wave resonator 800.

Mechanical circuit 812 includes an inductor L81, an inductor L82, acapacitor C82, and a resistor R82. Inductor L81 is magnetically coupledto inductor L80. Inductor L82, capacitor C82, and resistor R82 areconnected in series in this order between opposing ends of inductor L81.An inductance of inductor L82, a capacitance of capacitor C82, and aresistance value of resistor R82 are inertia M1, a reciprocal ofdistortion k1, and viscosity η1 of acoustic wave resonator 800 in FIG.4, respectively.

As voltage V1 is applied to electric circuit 811 by AC power supply 900,current Iw is input to acoustic wave resonator 800. A current Ie flowsthrough capacitor C0 and a current Iac flows through inductor L80.Current Iw is the sum of current Ie and current Iac.

As current Iac flows through inductor L80, an electric signal istransmitted from electric circuit 811 to mechanical circuit 812 throughmagnetic coupling between inductors L80 and L81. The electric signal isconverted to mechanical vibration and piezoelectric body 803 in FIG. 4is excited. Force F1 generated in acoustic wave resonator 800 and avelocity v1 of excitation can be considered as a voltage F1 and acurrent v1 generated in inductor L81 in mechanical circuit 812.

In contrast, when piezoelectric body 803 is excited and voltage F1 isgenerated in inductor L81, mechanical vibration is transmitted frommechanical circuit 812 to electric circuit 811 through magnetic couplingbetween inductors L80 and L81. Mechanical vibration is converted to anelectric signal and voltage V1 is generated in inductor L80 of electriccircuit 811. In mechanical circuit 812, force F1 is expressed withvelocity v1, inertia M1, distortion k1, and viscosity η1 as in anexpression (1) below.

$\begin{matrix}{F_{1} = {{M_{1}\frac{d\; v_{1}}{d\; t}} + {k_{1}{\int{v_{1}d\; t}}} + {\eta_{1}v_{1}}}} & (1)\end{matrix}$

FIG. 6 is an electrical equivalent circuit diagram of a Butterworth-VanDyke (BVD) model corresponding to acoustic wave resonator 800 in FIG. 4.Capacitor C0, voltage V1, current Iw, current Ie, and current Iac inFIG. 6 correspond to capacitor C0, voltage V1, current Iw, current Ie,and current Iac in FIG. 5, respectively. As shown in FIG. 6, acousticwave resonator 800 includes an electrical path 821 and an acoustic path822. Electrical path 821 and acoustic path 822 are connected in parallelbetween the opposing ends of AC power supply 900.

Electrical path 821 includes capacitor C0 connected between the opposingends of AC power supply 900. A damping capacitance of acoustic waveresonator 800 means a capacitance of capacitor C0 in electrical path821. Current Ie flows through electrical path 821.

Acoustic path 822 includes an inductor L1, a capacitor C1, and aresistor R1. Inductor L1, capacitor C1, and resistor R1 are connected inseries in this order between the opposing ends of AC power supply 900.Current Iac flows through acoustic path 822.

Voltage V1 is expressed with current Iac, an inductance of inductor L1,a capacitance of capacitor C1, and a resistance value of resistor R1 asin an expression (2) below.

$\begin{matrix}{V_{1} = {{L_{1}\frac{{dI}_{ac}}{d\; t}} + {\frac{1}{C_{1}}{\int{I_{ac}d\; t}}} + {R_{1}I_{ac}}}} & (2)\end{matrix}$

Regarding the expressions (1) and (2), when force F1 and velocity v1 inthe expression (1) are brought in correspondence with voltage V1 andcurrent Iac in the expression (2), the expressions (1) and (2) can beconsidered as expressions that express the same vibration phenomenon.Magnitude of excitation of piezoelectric body 803 in FIG. 4 is reflectedon magnitude of voltage V1 generated in acoustic path 822 in FIG. 6 andmagnitude of current Iac that flows through acoustic path 822.

Distortion caused by non-linearity of the elastic constant of acousticwave resonator 800 has been known to be in proportion to magnitude ofexcitation per unit area of the acoustic wave resonator. Magnitude ofexcitation per unit area of the acoustic wave resonator correlates withmagnitude of a current per unit area of acoustic path 822. Therefore,distortion caused by non-linearity of the elastic constant of acousticwave resonator 800 is in proportion to magnitude of a current per unitarea of acoustic path 822. An area of acoustic wave resonator 800 is inproportion to a capacitance (a damping capacitance) of capacitor C0.Therefore, distortion caused by the non-linearity of the elasticconstant of acoustic wave resonator 800 can be compared based oncomparison of a current density Jac defined as in an expression (3)below.

$\begin{matrix}{J_{ac} = \frac{I_{ac}}{C_{0}}} & (3)\end{matrix}$

As current density Jac expressed in the expression (3) is lower,distortion caused by the non-linearity of the elastic constant ofacoustic wave resonator 800 is smaller. Consequently, IMD resulting fromthe non-linearity can also be suppressed.

Referring again to FIG. 2, when a transmission signal is input toterminal T12 in multiplexer 1, a current corresponding to thetransmission signal from transmission filter 102 is input totransmission filter 101 and divided into currents to parallel armresonator p4 and serial arm resonator s3. Since a current density inparallel arm resonator p4 and serial arm resonator s3 can be lowered,distortion caused by the non-linearity of the elastic constant in eachresonator can be lessened and occurrence of IMD can be suppressed.

FIG. 7 is a diagram showing a frequency characteristic of an impedanceof acoustic wave resonator 800 in FIG. 6 and also a frequencycharacteristic of a current that flows through the acoustic waveresonator. In FIG. 7, frequencies fr and fa represent a resonancefrequency and an antiresonance frequency of the acoustic wave resonator.An impedance of the acoustic wave resonator attains to a relativeminimum at resonance frequency fr and to a relative maximum atantiresonance frequency fa. As the frequency is higher thanantiresonance frequency fa, the impedance of the acoustic wave resonatormoves clockwise on the Smith chart and becomes a capacitive impedance.

FIG. 7 (a) shows an impedance Zw of the acoustic wave resonator, afrequency characteristic of an impedance Ze of the electrical path, andalso a frequency characteristic of an impedance Zac of the acousticpath. FIG. 7 (b) shows a frequency characteristic of current Iw thatpasses through the acoustic wave resonator, a frequency characteristicof current Ie that flows through the electrical path, and also afrequency characteristic of current Iac that flows through the acousticpath.

As shown in FIG. 7 (a), impedance Zw of the acoustic wave resonator andimpedance Zac of the acoustic path attain to substantially 0 atresonance frequency fr. Resonance frequency fr is expressed withinductor L1 and capacitor C1 included in the acoustic path as in anexpression (4) below.

$\begin{matrix}{f_{r} = \frac{1}{2\; \pi \sqrt{L_{1}C_{1}}}} & (4)\end{matrix}$

As shown in FIG. 7 (b), substantially no current flows through theelectrical path at resonance frequency fr. Current Iac that flowsthrough the acoustic path at resonance frequency fr is substantially thesame as current Iw that passes through the acoustic wave resonator.

As shown in FIG. 7 (a), the impedance of the acoustic wave resonatorbecomes very high at antiresonance frequency fa. At antiresonancefrequency fa higher than resonance frequency fr, impedance Zac isinductive. Therefore, an impedance element included in the acoustic pathcan be approximated to a single inductor Lac. Antiresonance frequency fais expressed as a resonance frequency of an LC parallel resonancecircuit formed from inductor Lac and capacitor C0 in the electrical pathas in an expression (5) below.

$\begin{matrix}{f_{a} = \frac{1}{2\; \pi \sqrt{L_{ac}C_{0}}}} & (5)\end{matrix}$

As shown in FIG. 7 (b), current Iw that passes through the acoustic waveresonator attains to the relative minimum at antiresonance frequency fa.A current substantially the same in magnitude flows through theelectrical path and the acoustic path. This is because a currentcirculates through a circulation signal path formed by the acoustic pathand the electrical path in the acoustic wave resonator. In this case,the current in the electrical path and the current in the acoustic pathare opposite in phase to each other. Substantially no current passesthrough the acoustic wave resonator at antiresonance frequency fa. Arelatively high current, however, flows in the inside of the acousticwave resonator.

A phase of current Iac that flows through the acoustic path atantiresonance frequency fa is the same as the inverted phase of currentIe that flows through the electrical path. Currents Iac_fa and Ie_fa areexpressed with a current Iw_fa that passes through the acoustic waveresonator at antiresonance frequency fa, Qa which is a Q factor of theacoustic wave resonator at antiresonance frequency fa, and an imaginaryunit j, as in expressions (6) and (7) below, respectively.

I _(ac_fa) =−j·Q _(a) ·i _(w_fa)  (6)

I _(e_fa) =j·Q _(a) ·I _(w_fa)  (7)

Current Iac_fa that flows through the acoustic path at antiresonancefrequency fa is Qa times as high as a reference current Iw_fa which is acurrent that passes through the acoustic wave resonator. Therefore, inorder to lessen distortion caused by non-linearity of the elasticconstant of the acoustic wave resonator, reference current Iw_fa shouldbe lowered.

FIGS. 8(a)-8(c) are diagrams showing variation in frequencycharacteristic of an impedance of the acoustic wave generator, variationin frequency characteristic of a current through the acoustic path, andalso variation in frequency characteristic of a current density in theacoustic path when a fractional bandwidth of the acoustic wave resonatoris varied with a damping capacitance of the acoustic wave resonatorbeing constant.

FIG. 8 (a) is a diagram showing variation in frequency characteristic ofan impedance of the acoustic wave resonator when a fractional bandwidthof the acoustic wave resonator is varied with a damping capacitance ofthe acoustic wave resonator being constant. In FIG. 8 (a), thefractional bandwidth of the acoustic wave resonator is smaller in theorder of curves Z1 to Z4. As shown in FIG. 8 (a), with a resonancefrequency corresponding to each of curves Z1 to Z4 being constant, asthe fractional bandwidth is smaller, an antiresonance frequency of theacoustic wave resonator is lower and a difference between theantiresonance frequency and the resonance frequency is smaller.

FIG. 8 (b) is a diagram showing variation in frequency characteristic ofa current through the acoustic path when a fractional bandwidth of theacoustic wave resonator is varied with a damping capacitance of theacoustic wave resonator being constant. In FIG. 8 (b), curves Ia1 to Ia4correspond to curves Z1 to Z4 in FIG. 8 (a), respectively. As shown inFIG. 8 (b), as the fractional bandwidth is smaller, a current throughthe acoustic path at the antiresonance frequency is lower and thecurrent through the acoustic path is lower in a frequency band lowerthan the resonance frequency. The current through the acoustic path atthe resonance frequency is substantially constant without depending onthe fractional bandwidth.

FIG. 8 (c) is a diagram showing variation in frequency characteristic ofa current density in the acoustic path of the acoustic wave resonatorwhen a fractional bandwidth of the acoustic wave resonator is variedwith a damping capacitance of the acoustic wave resonator beingconstant. In FIG. 8 (c), curves Ja1 to Ja4 correspond to curves Z1 to Z4in FIG. 8 (a), respectively. As shown in FIG. 8 (c), as the fractionalbandwidth is smaller, a current density in the acoustic path at theantiresonance frequency is lower and the current density in the acousticpath is lower in a frequency band lower than the resonance frequency.The current density in the acoustic path at the resonance frequency issubstantially constant without depending on the fractional bandwidth.

Referring again to FIG. 2, a resonance circuit closer to common terminalT10 tends to be greater in distortion caused by non-linearity of theelastic constant of the acoustic wave resonator. Therefore, inmultiplexer 1, the fractional bandwidth of parallel arm resonator p4 ismade smaller than a maximum value of the fractional bandwidth of each ofserial arm resonators s1 to s3. Since the current density in parallelarm resonator p4 is lower than in an example where the fractionalbandwidth of parallel arm resonator p4 is greater than the maximum valueof the fractional bandwidth of each of serial arm resonators s1 to s3,occurrence of IMD can be suppressed. Consequently, deterioration ofreception sensitivity of multiplexer 1 can be suppressed.

It has been known that, when each acoustic wave resonator included inthe resonance circuit includes an IDT electrode, as a duty ratio of theacoustic wave resonator is higher, an IMD3 level of the resonancecircuit is higher as shown in FIG. 9. The duty ratio of the acousticwave resonator is an average value of duty ratios of a plurality ofelectrode fingers constituting the acoustic wave resonator. A duty ratioof the acoustic wave resonator including an interdigital transducer(IDT) electrode 830 as shown in FIG. 9 is a ratio of an electrode fingerwidth W1 to the sum of electrode finger width W1 and a gap G1 betweenelectrode fingers.

When each of parallel arm resonator p4 and serial arm resonators s1 tos3 is formed as the acoustic wave resonator including IDT electrode 830as shown in FIG. 9, a duty ratio of parallel arm resonator p4 isdesirably lower than a maximum value of a duty ratio of each of serialarm resonators s1 to s3.

An example in which each of the first filter and the second filter isthe transmission filter is described in the first embodiment. When twotypes of electric power different in frequency from each other are inputfrom the common terminal, a problem the same as in the first embodimentoccurs. Therefore, even though each of the first filter and the secondfilter is a reception filter, an effect the same as in the firstembodiment is achieved.

First Modification of First Embodiment

In a first modification of the first embodiment, a configuration forfurther lowering a current density in parallel arm resonator p4 byconnecting an impedance element in parallel to parallel arm resonator p4between parallel arm resonator p4 and common terminal T10 is described.

FIG. 11 is a circuit configuration diagram of a multiplexer 1A accordingto the first modification of the first embodiment. The configuration ofmultiplexer 1A is such that an inductor L11 and a capacitor C11 areadded to transmission filter 101 in multiplexer 1 in FIG. 2. Since theconfiguration is otherwise the same, description will not be repeated.

As shown in FIG. 11, inductor L11 is connected between phase shifter 110and a connection node between serial arm resonator s3 and parallel armresonator p4. Capacitor C11 is connected between the grounding point anda connection node among inductor L11, serial arm resonator s3, andparallel arm resonator p4. Capacitor C11 is connected in parallel toparallel arm resonator p4.

When a transmission signal is input to terminal T12, a currentcorresponding to the transmission signal from transmission filter 102 isinput to transmission filter 101. After the current passes throughinductor L11, it is divided into currents to capacitor C11, parallel armresonator p4, and serial arm resonator s3. Since the current is dividedalso into a current to capacitor C11, the current that passes throughparallel arm resonator p4 and serial arm resonator s3 can further belowered. Consequently, a current density in each of parallel armresonator p4 and serial arm resonator s3 can further be lowered.

Inductor L11 and capacitor C11 may be included not in transmissionfilter 101 but in phase shifter 110. Capacitor C11 may be connectedbetween the grounding point and a connection node between phase shifter110 and inductor L11. An inductor may be connected as an impedanceelement in parallel to parallel arm resonator p4. An impedance elementdoes not have to be connected between common terminal T10 and theconnection node between serial arm resonator s3 and parallel armresonator p4.

Second Modification of First Embodiment

In a second modification of the first embodiment, an example in which,by replacing parallel arm resonator p4 in FIG. 2 with a parallel armresonance circuit corresponding to a configuration where parallel armresonator p4 is divided in series, a current density in each parallelarm resonator included in the parallel arm resonance circuit is furtherlowered will be described.

FIG. 12 is a circuit configuration diagram of a multiplexer 1B accordingto the second modification of the first embodiment. The configuration ofmultiplexer 1B is such that parallel arm resonator p4 in FIG. 2 isreplaced with a parallel arm resonance circuit pc4. Since theconfiguration is otherwise the same, description will not be repeated.

As shown in FIG. 12, parallel arm resonance circuit pc4 includesparallel arm resonators p4A and p4B. Parallel arm resonators p4A and p4Bare connected in series between a grounding point and the connectionnode between phase shifter 110 and serial arm resonator s3.

FIG. 13 is an electrical equivalent circuit diagram of a BVD modelcorresponding to parallel arm resonance circuit pc4 in FIG. 12. As shownin FIG. 13, parallel arm resonator p4A includes an inductor L41, acapacitor C41, a resistor R41, and a capacitor C40A. Inductor L41,capacitor C41, and resistor R41 are connected in series in this orderbetween opposing terminals of capacitor C40A. A damping capacitance ofparallel arm resonator p4A is a capacitance of capacitor C40A.

Parallel arm resonator p4B includes an inductor L42, a capacitor C42, aresistor R42, and a capacitor C40B. Inductor L42, capacitor C42, andresistor R42 are connected in series in this order between opposingterminals of capacitor C40B. A damping capacitance of parallel armresonator p4B is a capacitance of capacitor C40B.

Parallel arm resonator p4A is equal in damping capacitance to parallelarm resonator p4B. A combined capacitance of parallel arm resonancecircuit pc4 is a combined capacitance of the damping capacitance ofparallel arm resonator p4A and the damping capacitance of parallel armresonator p4B. When the damping capacitance of parallel arm resonancecircuit pc4 is equal to the damping capacitance of parallel armresonator p4 in FIG. 2, the damping capacitance of each of parallel armresonators p4A and p4B is twice as high as the damping capacitance ofparallel arm resonator p4 because capacitor C40A and capacitor C40B areconnected in series. Consequently, the current density in each ofparallel arm resonators p4A and p4B can be lower than the currentdensity in parallel arm resonator p4 in FIG. 2. A duty ratio of parallelarm resonance circuit pc4 (an average value of duty ratios of parallelarm resonators p4A and p4B) is desirably lower than a maximum value of aduty ratio of each of serial arm resonators s1 to s3.

When a resonance circuit is formed from a single resonator, a combinedcapacitance of the resonance circuit means a damping capacitance of theresonator included in the resonance circuit. When a resonance circuit isformed from a plurality of resonators, a combined capacitance of theresonance circuit is calculated based on a damping capacitance of eachof the plurality of resonators included in the resonance circuit.

According to the multiplexer in the first embodiment and the first andsecond modifications above, deterioration of reception sensitivity canbe suppressed.

Second Embodiment

The multiplexer including two transmission filters and a singlereception filter is described in the first embodiment. In a secondembodiment, a multiplexer including two transmission filters and tworeception filters is described.

FIG. 14 is a circuit configuration diagram of a multiplexer 2 accordingto the second embodiment. As shown in FIG. 14, a multiplexer 2 includesa common terminal T20 (a common terminal), a terminal T21 (a firstterminal), a terminal T22 (a second terminal), a terminal T23 (a thirdterminal), a terminal T24 (a fourth terminal), a transmission filter 201(a first filter), a transmission filter 202 (a second filter), areception filter 203 (a third filter), a reception filter 204 (a fourthfilter), and a phase shifter 210.

Common terminal T20 is connected to phase shifter 210. Transmissionfilter 201 is connected to phase shifter 210 and terminal T21, betweencommon terminal T20 and terminal T21. Transmission filter 202 isconnected to phase shifter 210 and terminal T22, between common terminalT20 and terminal T22. Reception filter 203 is connected to phase shifter210 and terminal T23, between common terminal T20 and terminal T23.Reception filter 204 is connected to phase shifter 210 and terminal T24,between common terminal T20 and terminal T24. Phase shifter 210 may beprovided as necessary and it is not an essential feature.

A passband B1 (a first passband) of transmission filter 201 is from 1920to 1980 GHz. A passband B2 (a second passband) of transmission filter202 is from 1710 to 1785 GHz. A passband B3 (a third passband) ofreception filter 203 is from 2110 to 2170 GHz. A passband B4 (a fourthpassband) of reception filter 204 is from 1805 to 1880 GHz. Passbands B1to B4 correspond to Band1Tx, Band3Tx, Band1Rx, and Band3Rx defined underthe third generation partnership project (3GPP), respectively.Multiplexer 2 can simultaneously transmit from common terminal T20, asignal in passband B1 input from terminal T21 and a signal in passbandB2 input from terminal T22. In other words, multiplexer 2 is adapted to2ULCA.

With frequency f3 being defined as 2×f1−f2 with frequency f1 included inpassband B1 and frequency f2 included in passband B2, a range offrequency f3 is from 2130 to 2175 GHz. A part of the range of frequencyf3 overlaps passband B3 of reception filter 203. The range of frequencyf3 is a frequency band where IMD3 due to a signal from transmissionfilter 201 and a signal from transmission filter 202 occurs. Inmultiplexer 2, IMD3 due to two transmission signals occurs in passbandB3.

A lower limit frequency in the range of frequency f3 is a frequencycalculated by subtracting 1710 GHz representing a lower limit frequencyin passband B2 from twice 1920 GHz representing a lower limit frequencyin passband B1. An upper limit frequency in the range of frequency f3 isa frequency calculated by subtracting 1785 GHz representing an upperlimit frequency in passband B2 from twice 1980 GHz representing an upperlimit frequency in passband B1.

FIG. 15 is a diagram showing a specific circuit configuration oftransmission filter 201 in FIG. 14. As shown in FIG. 15, transmissionfilter 201 includes serial arm resonators s11 to s14 (a first serial armresonance circuit), parallel arm resonators p11 to p13, and a parallelarm resonator p14 (a first parallel arm resonance circuit). Transmissionfilter 201 is an acoustic wave filter formed from an acoustic waveresonator.

Serial arm resonators s11 to s14 are connected in series in this order,between terminal T21 and phase shifter 210. Parallel arm resonator p11is connected between a grounding point and a connection node betweenserial arm resonators s11 and s12. Parallel arm resonator p12 isconnected between the grounding point and a connection node betweenserial arm resonators s12 and s13. Parallel arm resonator p13 isconnected between the grounding point and a connection node betweenserial arm resonators s13 and s14. Parallel arm resonator p14 isconnected between the grounding point and a connection node betweenserial arm resonator s14 and phase shifter 210. No acoustic waveresonator is connected between common terminal T20 and parallel armresonator p14. Transmission filter 201 may further include an impedanceelement (a first impedance element) connected in parallel to parallelarm resonator p14, between the grounding point and common terminal T20.Parallel arm resonator p14 is smaller in fractional bandwidth thanserial arm resonator s14.

A transmission signal in passband B1 input from terminal T21 passesthrough transmission filter 201 and is reflected by transmission filter202, reception filter 203, and reception filter 204 and output fromcommon terminal T20.

A transmission signal in passband B2 input from terminal T22 passesthrough transmission filter 202 and is reflected by transmission filter201, reception filter 203, and reception filter 204 and output fromcommon terminal T20. Specifically, a current corresponding to thetransmission signal from transmission filter 202 is input totransmission filter 201 and divided into currents to parallel armresonator p14 and serial arm resonator s14. The transmission signal inpassband B2 is mainly reflected by parallel arm resonator p14 and serialarm resonator s14 and output from common terminal T20.

Multiplexer 2 is compared with a multiplexer according to a firstcomparative example below. A configuration of the multiplexer accordingto the first comparative example is such that parallel arm resonator p14is greater in fractional bandwidth than serial arm resonator s14, ascompared with the circuit configuration of multiplexer 2.

Table 1 below shows resonance frequency fr (MHz), antiresonancefrequency fa (MHz), fractional bandwidth BWR (%), a maximum value ofcurrent Iac (mA) through the acoustic path and a maximum value ofcurrent density Jac (mA/pF) in the acoustic path in each of passbands B1and B2, and a level DL3 (A²/pF³) of IMD3, of parallel arm resonators p11to p14 and serial arm resonators s11 to s14 of multiplexer 2.

TABLE 1 Acoustic wave Resonator p14 s14 p13 s13 p12 s12 p11 s11Resonance Frequency (fr) 1897.4 1939.7  1853.5 1963.5 1879.0 1946.21868.7 1938.8 Antiresonance Frequency (fa) 1944.8 2014.1  1925.3 2038.71951.6 2020.9 1940.9 2013.3 Fractional Bandwidth (BWR)    2.500   3.8393.871 3.830 3.862 3.836 3.866 3.839 Maximum Value of B2  103.6 39.1 45.110.1 12.0 1.0 1.2 0.2 Current (Iac) B1 1157.5 787.6  270.5 354.6 1157.3568.5 1029.8 652.6 Maximum Value of B2  46.1 33.5 34.8 13.3 3.1 0.8 0.30.0 Current Density (Jac) B1  515.0 673.4  208.7 464.7 302.9 438.7 258.9170.8 IMD3 Level (DL3)    0.0275   0.0177 0.0020 0.0022 0.0011 0.00020.0001 0.0000

Table 2 below shows resonance frequency fr (MHz), antiresonancefrequency fa (MHz), fractional bandwidth BWR (%), a maximum value ofcurrent Iac (mA) through the acoustic path and a maximum value ofcurrent density Jac (mA/pF) in the acoustic path in each of passbands B1and B2, and level DL3 (A²/pF³) of IMD3, of parallel arm resonators p11to p14 and serial arm resonators s11 to s14 of the multiplexer accordingto the first comparative example.

TABLE 2 Acoustic wave Resonator p14 s14 p13 s13 p12 s12 p11 s11Resonance Frequency (fr) 1907.6 1948.2  1867.8 1999.1 1880.5 1949.11872.3 1939.3 Antiresonance Freqnency (fa) 1981.1 2023.0  1940.0 2075.41953.1 2023.9 1944.6 2013.8 Fractional Bandwidth (BWR)    3.851   3.8363.866 3.816 3.861 3.835 3.864 3.839 Maximum Value of B2  68.7 55.6 55.215.6 22.4 1.3 1.4 0.2 Current (Iac) B1  777.3 823.6  374.1 240.4 1385.8498.7 1037.4 647.2 Maximum Value of B2  106.7 60.8 37.6 13.3 5.6 3.0 0.40.1 Current Density (Jac) B1 1206.2 900.4  254.9 204.2 345.0 1173.2260.2 446.4 IMD3 Level (DL3)    0.1000   0.0451 0.0036 0.0007 0.00270.0017 0.0001 0.0000

Level DL3 of IMD3 in Tables 1 and 2 is expressed as in an expression (8)below. This is also applicable to Tables 3 to 5 which will be describedlater. Max (Jac(f1)) represents a maximum value of current density Jacin passband B1. Max (Jac(f2)) represents a maximum value of currentdensity Jac in passband B2.

DL ₃=Max(J _(ac)(f ₁))²×Max(J _(ac)(f ₂))×C ₀  (8)

Based on comparison between Tables 1 and 2, multiplexer 2 is lower inIMD3 level of each of parallel arm resonator p14 and serial armresonator s14 than the multiplexer according to the first comparativeexample. Multiplexer 2 can achieve suppressed IMD3 as compared with themultiplexer in the first comparative example.

FIG. 16 is a diagram showing a pass characteristic (a frequencycharacteristic of insertion loss and an amount of attenuation) ofmultiplexer 2 in FIG. 15 and also a pass characteristic of a multiplexeraccording to the first comparative example. In FIG. 16, a solid linerepresents a pass characteristic of multiplexer 2 and a dotted linerepresents a pass characteristic of the multiplexer according to thefirst comparative example.

FIG. 16 (a) shows a pass characteristic from terminal T22 to commonterminal T20. FIG. 16 (b) shows a pass characteristic from commonterminal T20 to terminal T24. FIG. 16 (c) shows a pass characteristicfrom terminal T21 to common terminal T20. FIG. 16 (d) shows a passcharacteristic from common terminal T20 to terminal T23.

As shown in FIG. 16, in each of passbands B1 to B4 of multiplexer 2, apass characteristic comparable to the pass characteristic of themultiplexer according to the first comparative example is achieved.Multiplexer 2 can achieve suppressed IMD3 as compared with themultiplexer according to the first comparative example while itmaintains the pass characteristic.

Modification of Second Embodiment

In the second embodiment, a multiplexer including four terminalscorresponding to four respective filters is described. In a modificationof the second embodiment, a multiplexer in which two terminals connectedto two respective transmission filters are integrated into onetransmission terminal and two terminals connected to two respectivereception filters are integrated into one reception terminal isdescribed.

FIG. 17 is a circuit configuration diagram of a multiplexer 2A accordingto the modification of the second embodiment. The configuration ofmultiplexer 2A is such that terminals T21 and T24 of multiplexer 2 inFIG. 14 are replaced with connection nodes N21 and N24, respectively,and phase shifters 211 and 212 are added. Since the configuration isotherwise the same, description will not be repeated.

As shown in FIG. 17, phase shifter 211 is connected between transmissionfilter 201 and terminal T22 and connected between transmission filter202 and terminal T22. Phase shifter 212 is connected between receptionfilter 203 and terminal T23 and connected between reception filter 204and terminal T23. Transmission filter 201 and phase shifter 211 areconnected at connection node N21 (the first terminal). Reception filter204 and phase shifter 212 are connected at connection node N24 (thefourth terminal). Phase shifters 211 and 212 may be provided asnecessary and they are not essential features.

In multiplexer 2A, transmission terminals T21 and T22 of multiplexer 2in FIG. 14 are integrated into terminal T22 in FIG. 17. Receptionterminals T23 and T24 of multiplexer 2 in FIG. 14 are integrated intoterminal T23 in FIG. 17. According to the multiplexer in themodification of the second embodiment, the number of terminals can bedecreased and deterioration of reception sensitivity can be suppressed.

According to the multiplexer in the second embodiment and themodification above, deterioration of reception sensitivity can besuppressed.

Third Embodiment

An example in which one of two transmission filters is an acoustic wavefilter is described in the second embodiment. In a third embodiment, anexample in which each of the two transmission filters is an acousticwave filter is described.

FIG. 18 is a circuit configuration diagram of a multiplexer 3 accordingto the third embodiment. The configuration of multiplexer 3 is such thattransmission filter 202 of multiplexer 2 in FIG. 15 is replaced with atransmission filter 302 (a second filter). Since the configuration isotherwise the same, description will not be repeated.

As shown in FIG. 18, transmission filter 302 includes serial armresonators s21 to s24 (a second serial arm resonance circuit), parallelarm resonators p21 to p23, and a parallel arm resonator p24 (a secondparallel arm resonance circuit). Transmission filter 302 is an acousticwave filter formed from an acoustic wave resonator.

Serial arm resonators s21 to s24 are connected in series in this orderbetween terminal T22 and phase shifter 210. Parallel arm resonator p21is connected between a grounding point and a connection node betweenserial arm resonators s21 and s22. Parallel arm resonator p22 isconnected between the grounding point and a connection node betweenserial arm resonators s22 and s23. Parallel arm resonator p23 isconnected between the grounding point and a connection node betweenserial arm resonators s23 and s24. Parallel arm resonator p24 isconnected between the grounding point and a connection node betweenserial arm resonator s24 and phase shifter 210. No acoustic waveresonator is connected between common terminal T20 and parallel armresonator p24. Transmission filter 302 may further include an impedanceelement (a second impedance element) connected in parallel to parallelarm resonator p24, between the grounding point and common terminal T20.Parallel arm resonator p24 is smaller in fractional bandwidth thanserial arm resonator s24.

A transmission signal in passband B1 input from terminal T21 passesthrough transmission filter 201 and is reflected by transmission filter202, reception filter 203, and reception filter 204 and output fromcommon terminal T20. Specifically, a current corresponding to thetransmission signal from transmission filter 201 is input totransmission filter 202, and divided into currents to parallel armresonator p24 and serial arm resonator s24. The transmission signal inpassband B1 is mainly reflected by parallel arm resonator p24 and serialarm resonator s24 and output from common terminal T20. A process at thetime when a transmission signal in passband B2 is input from terminalT22 is the same as in the second embodiment.

Multiplexer 3 is compared with a multiplexer according to a secondcomparative example below. A configuration of the multiplexer accordingto the second comparative example is such that parallel arm resonatorp24 is greater in fractional bandwidth than serial arm resonator s24, ascompared with the circuit configuration of multiplexer 3.

Table 3 below shows fractional bandwidth BWR (%), a maximum value ofcurrent Iac (mA) through the acoustic path and a maximum value ofcurrent density Jac (mA/pF) in the acoustic path in each of passbands B1and B2, and level DL3 (A²/pF³) of IMD3, of parallel arm resonators p11to p14 and serial arm resonators s11 to s14 of multiplexer 3. Resonancefrequency fr (MHz) and antiresonance frequency fa (MHz) of each ofparallel arm resonators p11 to p14 and serial arm resonators s11 to s14of multiplexer 3 are the same as in Table 1. Table 3 shows resonancefrequency fr (MHz), antiresonance frequency fa (MHz), fractionalbandwidth BWR (%), a maximum value of current Iac (mA) through theacoustic path and a maximum value of current density Jac (mA/pF) in theacoustic path in each of passbands B1 and B2, and level DL3 (A²/pF³) ofIMD3, of parallel arm resonators p21 to p24 and serial arm resonatorss21 to s24 of multiplexer 3.

TABLE 3 Acoustic wave Resonator p14 s14 p13 s13 p12 s12 p11 s11Fractional Bandwidth (BWR)   2.500   3.839 3.871 3.830 3.862 3.836 3.8663.839 Maximum Value of B2 90.1  34.5 39.1 8.9 11.0 0.9 1.1 0.1 Current(Iac) B1 1150.7  798.6 268.9 359.5 1160.0 576.5 1025.8 661.7 MaximumValue of B2 40.1  29.5 30.2 11.7 2.9 0.7 0.3 0.0 Current Density (Jac)B1 511.9  682.8 207.5 471.1 303.6 444.9 257.9 173.2 IMD3 Level (DL3)  0.0236    0.0161 0.0017 0.0020 0.0010 0.0002 0.0001 0.0000 Acousticwave Resonator p24 s24 p23 s23 p22 s22 p21 s21 Resonance Frequency (fr)1675.3  1733.6  1674.1 1756.0 1687.6 1751.6 1676.7 1743.2 AntiresonanceFrequency (fa) 1717.2  1801.5  1740.1 1824.6 1754.0 1820.1 1742.7 1811.4Fractional Bandwidth (BWR)   2.500   3.917 3.939 3.908 3.934 3.910 3.9383.913 Maximum Value of B2 189.6  1579.1  1083.9 516.2 1235.5 637.21116.7 764.5 Current (Iac) B1 22.6 121.9 64.7 26.5 13.3 3.0 1.3 0.6Maximum Value of B2 218.9  390.1 325.4 596.1 320.2 742.6 284.9 304.0Current Density (Jac) B1 26.1  30.1 19.4 30.6 3.4 3.4 0.3 0.3 IMD3 Level(DL3)   0.0001    0.0014 0.0004 0.0005 0.0000 0.0000 0.0000 0.0000

Table 4 below shows fractional bandwidth BWR (%), a maximum value ofcurrent Iac (mA) through the acoustic path and a maximum value ofcurrent density Jac (mA/pF) in the acoustic path in each of passbands B1and B2, and level DL3 (A²/pF³) of IMD3, of parallel arm resonators p11to p14 and serial arm resonators s11 to s14 of the multiplexer accordingto the second comparative example. Resonance frequency fr (MHz) andantiresonance frequency fa (MHz) of each of parallel arm resonators p11to p14 and serial arm resonators s11 to s14 of multiplexer 3 are thesame as in Table 1. Table 4 shows resonance frequency fr (MHz),antiresonance frequency fa (MHz), fractional bandwidth BWR (%), amaximum value of current Iac (mA) through the acoustic path and amaximum value of current density Jac (mA/pF) in the acoustic path ineach of passbands B1 and B2, and level DL3 (A²/pF³) of IMD3, of parallelarm resonators p21 to p24 and serial arm resonators s21 to s24 of themultiplexer according to the second comparative example.

TABLE 4 Acoustic wave Resonator p14 s14 p13 s13 p12 s12 p11 s11Fractional Bandwidth (BWR)   2.500   3.839 3.871 3.830 3.862 3.836 3.8663.839 Maximum Value of B2 103.6 39.1 45.1 10.1 12.0 1.0 1.2 0.2 Current(Iac) B1 1157.5  787.6  270.5 354.6 1157.3 568.5 1029.8 652.6 MaximumValue of B2  46.1 33.5 34.8 13.3 3.1 0.8 0.3 0.0 Current Density (Jac)B1 515.0 673.4  208.7 464.7 302.9 438.7 258.9 170.8 IMD3 Level (DL3)   0.0275   0.0177 0.0020 0.0022 0.0011 0.0002 0.0001 0.0000 Acousticwave Resonator p24 s24 p23 s23 p22 s22 p21 s21 Resonance Frequency (fr)1694.5  1755.7  1677.0 1745.6 1675.5 1744.7 1671.7 1745.8 AntiresonanceFrequency (fa) 1761.1  1824.3  1743.1 1813.9 1741.5 1813.0 1737.6 1814.1Fractional Bandwidth (BWR)   3.931   3.908 3.938 3.912 3.938 3.912 3.9403.912 Maximum Value of B2 317.3 584.6  1212.3 762.6 868.7 736.6 856.1664.6 Current (Iac) B1  18.4 54.9 24.2 7.5 3.7 1.2 0.6 0.4 Maximum Valueof B2 695.0 870.2  1250.4 786.5 643.0 545.2 245.6 190.7 Current Density(Jac) B1  40.2 81.8 25.0 7.8 2.7 0.9 0.2 0.1 IMD3 Level (DL3)    0.0005  0.0039 0.0008 0.0000 0.0000 0.0000 0.0000 0.0000

Based on comparison between Tables 1 and 4, the multiplexer according tothe second comparative example is equal in IMD3 level of each ofparallel arm resonator p14 and serial arm resonator s14 to themultiplexer according to the second embodiment. Based on comparisonbetween Tables 3 and 4, multiplexer 3 is lower in IMD3 level of each ofparallel arm resonators p14 and p24 and serial arm resonators s14 ands24 than the multiplexer according to the second comparative example.Multiplexer 3 can achieve suppressed IMD3 as compared with themultiplexer according to the second comparative example and themultiplexer according to the second embodiment.

FIG. 19 is a diagram showing a pass characteristic of multiplexer 3 inFIG. 18 and also a pass characteristic of the multiplexer according tothe second comparative example. In FIG. 19, a solid line shows a passcharacteristic of multiplexer 3 and a dotted line shows a passcharacteristic of the multiplexer according to the second comparativeexample.

FIG. 19 (a) shows a pass characteristic from terminal T22 to commonterminal T20. FIG. 19 (b) shows a pass characteristic from commonterminal T20 to terminal T24. FIG. 19 (c) shows a pass characteristicfrom terminal T21 to common terminal T20. FIG. 19 (d) shows a passcharacteristic from common terminal T20 to terminal T23.

As shown in FIG. 19, in each of passbands B1 to B4 of multiplexer 3, apass characteristic comparable to the pass characteristic of themultiplexer according to the second comparative example is achieved.Multiplexer 3 can achieve suppressed IMD3 as compared with themultiplexer according to the second comparative example and themultiplexer according to the second embodiment while it maintains thepass characteristic.

Modification of Third Embodiment

As shown in FIG. 19, passband B4 (1805 to 1880 GHz) of reception filter204 is a frequency band between passband B1 (1920 to 1980 GHz) oftransmission filter 201 and passband B2 (1710 to 1785 GHz) oftransmission filter 202.

Normally, an antiresonance frequency of a serial arm resonator includedin transmission filter 202 is higher than passband B2. An antiresonancefrequency of a parallel arm resonator included in transmission filter201 is often set around a lower limit of passband B1. Since each of anantiresonance frequency of a serial arm resonator included intransmission filter 202 and an antiresonance frequency of a parallel armresonator included in transmission filter 201 is often close to passbandB4, a current density in an acoustic wave resonator included inreception filter 204 tends to be high based on the expressions (3) and(6). Consequently, IMD3 due to two transmission signals generated inpassband B4 tends to be great. Therefore, a reception filter havingpassband B4 is desirably configured to be able to suppress IMD,similarly to two transmission filters.

In a modification of the third embodiment, an example in which areception filter having passband B4 is an acoustic wave filterconfigured to be able to suppress IMD similarly to two transmissionfilters is described. A multiplexer according to the modification of thethird embodiment can achieve suppressed IMD in the reception filterhaving passband B4 and hence it can achieve suppressed deterioration ofreception sensitivity as compared with the multiplexer in the thirdembodiment.

FIG. 20 is a circuit configuration diagram of a multiplexer 3A accordingto the modification of the third embodiment. The configuration ofmultiplexer 3A is such that transmission filter 204 of multiplexer 3 inFIG. 18 is replaced with a reception filter 304 (a fourth filter). Sincethe configuration is otherwise the same, description will not berepeated.

As shown in FIG. 20, reception filter 304 includes serial arm resonatorss41 to s44 (a third serial arm resonance circuit), parallel armresonators p41 to p43, and a parallel arm resonator p44 (a thirdparallel arm resonance circuit). Reception filter 304 is an acousticwave filter formed from an acoustic wave resonator.

Serial arm resonators s41 to s44 are connected in series in this orderbetween terminal T24 and phase shifter 210. Parallel arm resonator p41is connected between a grounding point and a connection node betweenserial arm resonators s41 and s42. Parallel arm resonator p42 isconnected between the grounding point and a connection node betweenserial arm resonators s42 and s43. Parallel arm resonator p43 isconnected between the grounding point and a connection node betweenserial arm resonators s43 and s44. Parallel arm resonator p44 isconnected between the grounding point and a connection node betweenserial arm resonator s44 and phase shifter 210. No acoustic waveresonator is connected between common terminal T20 and parallel armresonator p44. A parallel arm resonance circuit corresponding to such aconfiguration that parallel arm resonator p44 is divided in series maybe provided instead of parallel arm resonator p44. Reception filter 304may further include an impedance element (a third impedance element)connected in parallel to parallel arm resonator p44, between thegrounding point and common terminal T20. A fractional bandwidth ofparallel arm resonator p44 is smaller than a maximum value of afractional bandwidth of each of serial arm resonators s41 to s44.

When a transmission signal in passband B1 is input to terminal T21 and atransmission signal in passband B2 is input to terminal T22, a currentcorresponding to the transmission signal from transmission filter 201and a current corresponding to the transmission signal from transmissionfilter 202 are input to reception filter 304 and divided into currentsto parallel arm resonator p44 and serial arm resonator s44. Thetransmission signal in passband B1 and the transmission signal inpassband B2 are mainly reflected by parallel arm resonator p44 andserial arm resonator s44 and output from common terminal T20.

The multiplexer according to the third embodiment and the modificationabove can achieve suppressed deterioration of reception sensitivity ascompared with the multiplexer according to the second embodiment.

Fourth Embodiment

In a fourth embodiment, an example in which each of two transmissionfilters includes a parallel arm resonance circuit corresponding to sucha configuration that a single parallel arm resonator is divided inseries is described.

FIG. 21 is a circuit configuration diagram of a multiplexer 4 accordingto the fourth embodiment. The configuration of multiplexer 4 is suchthat transmission filters 201 and 302 of multiplexer 3 in FIG. 18 arereplaced with transmission filters 401 and 402, respectively. Aconfiguration of transmission filter 401 is such that parallel armresonator p14 of transmission filter 201 in FIG. 18 is replaced withparallel arm resonance circuit pc14. A configuration of transmissionfilter 402 is such that parallel arm resonator p24 of transmissionfilter 302 in FIG. 18 is replaced with a parallel arm resonance circuitpc24. Since the configuration is otherwise the same, description willnot be repeated.

As shown in FIG. 21, parallel arm resonance circuit pc14 includesparallel arm resonators p141 and p142. Parallel arm resonators p141 andp142 are connected in series between a grounding point and phase shifter210.

Parallel arm resonance circuit pc14 is smaller in fractional bandwidththan serial arm resonator s14. Each of parallel arm resonators p141 andp142 has a damping capacitance twice as high as the damping capacitanceof parallel arm resonance circuit pc14.

Parallel arm resonance circuit pc24 includes parallel arm resonatorsp241 and p242. Parallel arm resonators p241 and p242 are connected inseries between a grounding point and phase shifter 210.

Parallel arm resonance circuit pc24 is smaller in fractional bandwidththan serial arm resonator s24. Each of parallel arm resonators p241 andp242 has a damping capacitance twice as high as the damping capacitanceof parallel arm resonance circuit pc24.

Table 5 below shows fractional bandwidth BWR (%), a maximum value ofcurrent Iac (mA) through the acoustic path and a maximum value ofcurrent density Jac (mA/pF) in the acoustic path in each of passbands B1and B2, and level DL3 (A²/pF³) of IMD3, of parallel arm resonators p11to p13, parallel arm resonance circuit pc14, and serial arm resonatorss11 to s14 of multiplexer 4. Resonance frequency fr and antiresonancefrequency fa of each of parallel arm resonators p11 to p13 and serialarm resonators s11 to s14 of multiplexer 4 are the same as values shownin Table 1. Resonance frequency fr and antiresonance frequency fa ofparallel arm resonance circuit pc14 are the same as values of parallelarm resonator p14 in Table 1.

Table 5 shows fractional bandwidth BWR (%), a maximum value of currentIac (mA) through the acoustic path and a maximum value of currentdensity Jac (mA/pF) in the acoustic path in each of passbands B1 and B2,and level DL3 (A²/pF³) of IMD3, of parallel arm resonators p21 to p23,parallel arm resonance circuit pc24, and serial arm resonators s21 tos24 of multiplexer 4. Resonance frequency fr and antiresonance frequencyfa of each of parallel arm resonators p21 to p23 and serial armresonators s21 to s24 of multiplexer 4 are the same as values shown inTable 3. Resonance frequency fr and antiresonance frequency fa ofparallel arm resonance circuit pc24 are the same as values of parallelarm resonator p24 in Table 3.

TABLE 5 Acoustic wave Resonator pc14 s14 p13 s13 p12 s12 p11 s11Fractional Bandwidth (BWR)   2.500   3.839 3.871 3.830 3.862 3.836 3.8663.839 Maximum Value of B2 90.1  34.5 39.1 8.9 11.0 0.9 1.1 0.1 Current(Iac) B1 1150.7  798.6 268.9 359.5 1160.0 576.5 1025.8 661.7 MaximumValue of B2 20.0  29.5 30.2 11.7 2.9 0.7 0.3 0.0 Current Density (Jac)B1 256.0  682.8 207.5 471.1 303.6 444.9 257.9 173.2 IMD3 Level (DL3)  0.0059    0.0161 0.0017 0.0020 0.0010 0.0002 0.0001 0.0000 Acousticwave Resonator pc24 s24 p23 s23 p22 s22 p21 s21 Fractional Bandwidth(BWR)   2.500   3.917 3.939 3.908 3.934 3.910 3.938 3.913 Maximum Valueof B2 189.6  1579.1  1083.9 516.2 1235.5 637.2 1116.7 764.5 Current(Iac) B1 22.6 121.9 64.7 26.5 13.3 3.0 1.3 0.6 Maximum Value of B2109.4  390.1 325.4 596.1 320.2 742.6 284.9 304.0 Current Density (Jac)B1 13.1  30.1 19.4 30.6 3.4 3.4 0.3 0.3 IMD3 Level (DL3)   0.0000   0.0014 0.0004 0.0005 0.0000 0.0000 0.0000 0.0000

Based on comparison between Tables 3 and 5, the IMD3 levels of serialarm resonators s14 and s24 of multiplexer 4 are as high as the IMD3levels of serial arm resonators s14 and s24 of multiplexer 3, whereasthe IMD3 levels of parallel arm resonance circuits pc14 and pc24 ofmultiplexer 4 are lower than the IMD3 levels of parallel arm resonatorsp14 and p24 of multiplexer 3. Multiplexer 4 can achieve suppressed IMD3as compared with multiplexer 3.

The multiplexer according to the fourth embodiment above can achievesuppressed deterioration of reception sensitivity as compared with themultiplexer according to the third embodiment.

Fifth Embodiment

In a fifth embodiment, a radio-frequency front end circuit and acommunication apparatus that can be implemented by using themultiplexers according to the first to fourth embodiments and themodifications are described.

FIG. 22 is a configuration diagram of a communication apparatus 5according to the fifth embodiment. As shown in FIG. 22, communicationapparatus 5 includes an antenna element 510, a radio-frequency front endcircuit 520, a radio frequency (RF) signal processing circuit 530, and abaseband integrated circuit (BBIC) 540.

Radio-frequency front end circuit 520 includes a switch 521,multiplexers 2A and 2B according to the second embodiment, transmissionamplification circuits 51T to 54T, and reception amplification circuits51R to 54R. Radio-frequency front end circuit 520 may include themultiplexer according to the first, third, or fourth embodiment or themodifications.

Switch 521 is connected between antenna element 510 and multiplexer 2Aand connected between antenna element 510 and multiplexer 2B. Switch 521switches a multiplexer to which antenna element 510 is to be connected,between multiplexers 2A and 2B.

Transmission amplification circuits 51T and 52T are power amplifiersthat amplify power of a radio-frequency signal in a prescribed frequencyband from RF signal processing circuit 530 and output power tomultiplexer 2A. Transmission amplification circuits 53T and 54T arepower amplifiers that amplify power of a radio-frequency signal in aprescribed frequency band from RF signal processing circuit 530 andoutput power to multiplexer 2B.

Reception amplification circuits 51R and 52R are low noise amplifiersthat amplify power of a radio-frequency signal in a prescribed frequencyband from multiplexer 2A and output power to RF signal processingcircuit 530. Reception amplification circuits 53R and 54R are low noiseamplifiers that amplify power of a radio-frequency signal in aprescribed frequency band from multiplexer 2B and output power to RFsignal processing circuit 530.

Transmission amplification circuits 51T and 52T and receptionamplification circuits 51R and 52R are connected in parallel between RFsignal processing circuit 530 and multiplexer 2A. Transmissionamplification circuits 53T and 54T and reception amplification circuits53R and 54R are connected in parallel between RF signal processingcircuit 530 and multiplexer 2B.

RF signal processing circuit 530 processes radio-frequency signalstransmitted and received by antenna element 510. Specifically, RF signalprocessing circuit 530 processes a radio-frequency signal input fromantenna element 510 through a reception-side signal path by downconversion and outputs the processed signal to BBIC 540. RF signalprocessing circuit 530 processes a transmission signal input from BBIC540 by up conversion and output the processed signal.

The communication apparatus according to the fifth embodiment above canachieve suppressed deterioration of reception sensitivity of themultiplexer and can achieve improved communication quality.

The embodiments disclosed herein are intended also to be carried out asbeing combined as appropriate unless such combination is inconsistent.It should be understood that the embodiments disclosed herein areillustrative and non-restrictive in every respect. The scope of thepresent disclosure is defined by the terms of the claims rather than thedescription above and is intended to include any modifications withinthe scope and meaning equivalent to the terms of the claims.

What is claimed is:
 1. A multiplexer comprising: a common terminal, afirst terminal, a second terminal, and a third terminal; a first filterconnected between the common terminal and the first terminal, the firstfilter having a first passband; a second filter connected between thecommon terminal and the second terminal, the second filter having asecond passband not overlapping the first passband; and a third filterconnected between the common terminal and the third terminal, the thirdfilter having a third passband overlapping neither the first passbandnor the second passband, with a frequency f3 being defined as M×f1±N×f2or M×f2±N×f1, M and N being natural numbers, f1 being a frequencyincluded in the first passband and f2 being a frequency included in thesecond passband, at least a part of a range of the frequency f3overlapping the third passband, the first filter including at least onefirst serial arm resonance circuit connected between the common terminaland the first terminal, and a first parallel arm resonance circuitconnected between the common terminal and a grounding point, the firstparallel arm resonance circuit including at least one acoustic waveresonator, no acoustic wave resonator being connected between the commonterminal and the first parallel arm resonance circuit, and under acondition that a value calculated by dividing a difference between anantiresonance frequency and a resonance frequency of a resonance circuitby the resonance frequency is defined as a fractional bandwidth of theresonance circuit, a fractional bandwidth of the first parallel armresonance circuit being smaller than a maximum value of a fractionalbandwidth of each of the at least one first serial arm resonancecircuit.
 2. The multiplexer according to claim 1, wherein the frequencyf3 being 2×f1−f2.
 3. The multiplexer according to claim 1, wherein thefirst parallel arm resonance circuit includes two acoustic waveresonators connected in series between the common terminal and thegrounding point.
 4. The multiplexer according to claim 1, wherein thefirst filter further includes a first impedance element connected inparallel to the first parallel arm resonance circuit, between thegrounding point and the common terminal.
 5. The multiplexer according toclaim 1, wherein the second filter includes at least one second serialarm resonance circuit connected between the common terminal and thesecond terminal and a second parallel arm resonance circuit connectedbetween the common terminal and the grounding point and including atleast one acoustic wave resonator, no acoustic wave resonator beingconnected between the common terminal and the second parallel armresonance circuit, and a fractional bandwidth of the second parallel armresonance circuit being smaller than a maximum value of a fractionalbandwidth of each of the at least one second serial arm resonancecircuit.
 6. The multiplexer according to claim 5, wherein the secondparallel arm resonance circuit includes two acoustic wave resonatorsconnected in series between the common terminal and the grounding point.7. The multiplexer according to claim 5, wherein the second filterfurther includes a second impedance element connected in parallel to thesecond parallel arm resonance circuit, between the grounding point andthe common terminal.
 8. The multiplexer according to claim 1, furthercomprising: a fourth terminal; and a fourth filter connected between thecommon terminal and the fourth terminal, the fourth filter having afourth passband overlapping none of the first passband, the secondpassband, and the third passband, wherein the fourth passband is afrequency band between the first passband and the second passband, thefourth filter includes at least one third serial arm resonance circuitconnected between the common terminal and the fourth terminal and athird parallel arm resonance circuit connected between the commonterminal and the grounding point and including at least one acousticwave resonator, no acoustic wave resonator is connected between thecommon terminal and the third parallel arm resonance circuit, and afractional bandwidth of the third parallel arm resonance circuit beingsmaller than a maximum value of a fractional bandwidth of each of the atleast one third serial arm resonance circuit.
 9. The multiplexeraccording to claim 8, wherein the third parallel arm resonance circuitincludes two acoustic wave resonators connected in series between thecommon terminal and the grounding point.
 10. The multiplexer accordingto claim 8, wherein the third filter further includes a third impedanceelement connected in parallel to the third parallel arm resonancecircuit, between the grounding point and the common terminal.
 11. Themultiplexer according to claim 1, wherein any acoustic wave resonatorsincluded in the at least one first serial arm resonance circuit and thefirst parallel arm resonance circuit being an IDT electrode acousticwave resonator that includes an IDT electrode formed from a plurality ofelectrode fingers, and under a condition that a duty ratio of the IDTelectrode acoustic wave resonator is defined as a ratio of a width ofeach of the plurality of electrode fingers to a sum of the width and aninterval between adjacent electrode fingers included in the plurality ofelectrode fingers, a duty ratio of the at least one acoustic waveresonator included in the first parallel arm resonance circuit is lowerthan a duty ratio of at least one acoustic wave resonator included inthe first serial arm resonance circuit.
 12. The multiplexer according toclaim 1, further comprising: a phase shifter connected between thecommon terminal and at least one of the first filter, the second filterand the third filter.
 13. The multiplexer according to claim 12, furthercomprising: another phase shifter connected between the second filterand the second terminal.
 14. The multiplexer according to claim 1,further comprising: means for suppressing intermodulation distortionresulting from a non-linearity of an elastic constant of the at leastone acoustic wave resonator of the first parallel arm resonance circuit.15. The multiplexer according to claim 14, wherein the means forsuppresing comprises configuring the parallel arm resonance circuit tohave a current density smaller than a maximum value of a current densityin each serial arm resonance circuit of the at least one first serialarm resonance circuit.
 16. A radio-frequency front end circuitcomprising: a multiplexer including a common terminal, a first terminal,a second terminal, and a third terminal, a first filter connectedbetween the common terminal and the first terminal, the first filterhaving a first passband, a second filter connected between the commonterminal and the second terminal, the second filter having a secondpassband not overlapping the first passband, and a third filterconnected between the common terminal and the third terminal, the thirdfilter having a third passband overlapping neither the first passbandnor the second passband, with a frequency f3 being defined as M×f1±N×f2or M×f2±N×f1, M and N being natural numbers, f1 being a frequencyincluded in the first passband and f2 being a frequency included in thesecond passband, at least a part of a range of the frequency f3overlapping the third passband, the first filter including at least onefirst serial arm resonance circuit connected between the common terminaland the first terminal, and a first parallel arm resonance circuitconnected between the common terminal and a grounding point, the firstparallel arm resonance circuit including at least one acoustic waveresonator, no acoustic wave resonator being connected between the commonterminal and the first parallel arm resonance circuit, and under acondition that a value calculated by dividing a difference between anantiresonance frequency and a resonance frequency of a resonance circuitby the resonance frequency is defined as a fractional bandwidth of theresonance circuit, a fractional bandwidth of the first parallel armresonance circuit being smaller than a maximum value of a fractionalbandwidth of each of the at least one first serial arm resonancecircuit; and an amplification circuit electrically connected to themultiplexer.
 17. The radio-frequency front end circuit, wherein thefrequency f3 being 2×f1−f2.
 18. A communication apparatus comprising: anantenna element; an RF signal processing circuit that processes aradio-frequency signal transmitted and received by the antenna element;and a radio-frequency front end circuit that transmits theradio-frequency signal between the antenna element and the RF signalprocessing circuit, the radio-frequency front end circuit including amultiplexer including a common terminal, a first terminal, a secondterminal, and a third terminal, a first filter connected between thecommon terminal and the first terminal, the first filter having a firstpassband, a second filter connected between the common terminal and thesecond terminal, the second filter having a second passband notoverlapping the first passband, and a third filter connected between thecommon terminal and the third terminal, the third filter having a thirdpassband overlapping neither the first passband nor the second passband,with a frequency f3 being defined as M×f1±N×f2 or M×f2±N×f1, M and Nbeing natural numbers, f1 being a frequency included in the firstpassband and f2 being a frequency included in the second passband, atleast a part of a range of the frequency f3 overlapping the thirdpassband, the first filter including at least one first serial armresonance circuit connected between the common terminal and the firstterminal, and a first parallel arm resonance circuit connected betweenthe common terminal and a grounding point, the first parallel armresonance circuit including at least one acoustic wave resonator, noacoustic wave resonator being connected between the common terminal andthe first parallel arm resonance circuit, and under a condition that avalue calculated by dividing a difference between an antiresonancefrequency and a resonance frequency of a resonance circuit by theresonance frequency is defined as a fractional bandwidth of theresonance circuit, a fractional bandwidth of the first parallel armresonance circuit being smaller than a maximum value of a fractionalbandwidth of each of the at least one first serial arm resonancecircuit; and an amplification circuit electrically connected to themultiplexer.
 19. The communication apparatus of claim 18, wherein thefrequency f3 being 2×f1−f2.